I switched to using CBC's Mauril from Duolingo, and it's been good for me. However, it's only available to Canadian residents (or VPN users) and it's only for French. So it worked for me but obviously that covers a small subset of Duolingo users.
I actually wrote a script to figure out what the last G stands for. The last G stsnds for "RangeError: Maximum call stack size exceeded". Pretty weird.
Copilot does do reviews in Github now. And they're decent actually, in my experience.